Sinapis alba has successfully been grown as a condiment crop on the western Canadian prairie for many years. It has many agronomic advantages for dryland production over Brassica napus, B. rapa and B. juncea. The most important aspect is its excellent heat and drought tolerance. Seed pods are highly shatter-resistant allowing direct combining of the crop. Sinapis alba is highly resistant to blackleg disease, a serious disease of B. napus canola. It also has useful levels of flea beetle resistance, a serious pest of B. napus and B. rapa and can survive moderate flea beetle attack without insecticidal protection, thereby reducing or eliminating the need for insecticides against flea beetle. Sinapis alba is large seeded (5-6 g per 1000 seeds) compared to the Brassica oilseeds (2.5-3.5 g per 1000 seeds). This larger seed size allows S. alba to be planted into moisture up to a 50 mm depth, whereas shallow seeding is required for Brassica type crops. Sinapis alba seed is of a bright yellow colour, a much-desired trait in the typically black-seeded B. napus species.
Despite the many agronomic advantages of S. alba, it is not grown as an oilseed in Canada, because the seed is relatively high in erucic acid (C22:1) and glucosinolate content and has a low oil content (about 28%). Sinapis alba seed oil of condiment mustard varieties such as AC Pennant contains about 35% erucic acid (Downey and Rakow 1995). Although erucic acid toxicity has not been demonstrated in humans, this fatty acid has been associated with poor performance and abnormal lipid metabolism in heart and skeletal muscle tissue in laboratory animals and pigs.
Both, a line with 3-4% by weight erucic acid (e.g. BHL3-926), and a high erucic acid variety having an erucic acid content over 55% (for example ‘Sabre’) S. alba strains have been developed at the Agriculture and Agri-Food Canada, Saskatoon Research Centre. Sinapis alba lines having very low p-hydroxybenzyl glucosinolate are known, e.g. (Brown et al. 1999, Krzymanski et al. 1991, and Raney et al. 1995a & 1995b). However, these lines have elevated levels of 2-hydroxy-3-butenyl glucosinolate and benzyl glucosinolate thereby limiting the utility of oil-free meal prepared from these oil seeds following oil extraction. Glucosinolates reduce palatability and feed intake in non-runinant animals, and inhibit iodine uptake by the thyroid gland, causing goitre and other growth and reproductive anomalies. Of particular concern is benzyl glucosinolate which is not found in canola (B. napus and B. rapa) or mustard (B. juncea and S. alba) and therefore may have other possible deleterious properties. In order to ensure the success of S. alba as an agricultural crop, the oil must exhibit desired properties for either human or industrial use, and the seed meal should also have a high value use, for example, in livestock or fish feed formulations or in human processed food products.
The oil free meal in S. alba possesses a relatively high protein content (45-48%) and the amino acid composition of the meal is fairly well balanced. Compared to soybean and canola, S. alba protein contains less of the amino acid lysine, but more of the sulphur amino acids methionine and cystine. The high concentration of glucosinolates in S. alba meal has discouraged its use in animal feed formulations. Sinapis alba has found use in human food applications as a condiment and, because of its relatively high protein and mucilage content, in prepared foods as an animal protein extender, binding agent or emulsifying agent. Such uses require only limited acres of S. alba to satisfy demand.
Therefore, for S. alba to become a high quality edible oilseed crop, low erucic acid strains, with a high oil content, preferably with a high oleic acid and low linolenic acid content, need to be developed. To ensure that the oil-free meal may be used as an animal feed, then the total glucosinolate level (responsible for the bitter taste of S. alba seed) within such lines must be as low as possible. Furthermore, to produce quality industrial oils, S. alba oil seed comprising high levels of erucic acid, with low glucosinolate levels are also required, ensuring market acceptability for both the extracted oil, and the oil-free meal.
Brassica napus L. (Argentine canola) is an important edible oil crop. The area planted to canola in western Canada was 4,052,400 hectares annually, average for the 10-year period 1989 to 1998, 90% of which is B. napus. The area of production for B. napus is limited because canola has limited heat and drought tolerance. Therefore, alternate sources of plant oil produced from a hardier plant, for example from S. alba, is desired. However, to be commercially acceptable, the oil and meal produced by S. alba must exhibit the minimum standard of characteristics found within that prepared from B. napus. 
Sinapis alba and Brassica species are very different in the types of glucosinolates present in their seeds. The major glucosinolate in Sinapis alba seed is p-hydroxybenzyl glucosinolate (140-150 μmoles per g of seed), which gives S. alba seed its bitter taste. It is not found in Brassica species seed such as B. napus, B. rapa, B. juncea, or B. carinata. Brassica species seed contain high concentrations of allyl, 3-butenyl, 4-pentenyl, 2-hydroxy-3-butenyl and 2-hydroxy-4-pentenyl glucosinolates totalling 100 μmoles per gram of seed or more. In canola strains of these species, except for B. carinata which so far no low glucosinolate lines have been developed, the total glucosinolate content is much reduced (less than 18 μmoles per g seed).
Low glucosinolate S. alba lines have been developed comprising total glucosinolate contents ranging from about 15 μmoles per g seed to about 40 μmoles per g seed (Krzymanski et al. 1991). In addition to low levels of p-hydroxybenzyl glucosinolate, these varieties also contain 5-10 μmoles per g of seed of 2-hydroxy-3-butenyl glucosinolate and benzyl glucosinolate. These low glucosinolate S. alba lines have normal erucic acid contents (approx. 28% by weight) in their seed oil.
The erucic acid content in S. alba is controlled by a single gene exhibiting partial dominance of high over zero erucic acid contents (Drost et al. 1999a; Brown et al., 1999). Similarly, the inheritance of p-hydroxybenzyl glucosinolate is also controlled by a single gene with high p-hydroxybenzyl glucosinolate content dominant over low p-hydroxybenzyl glucosinolate content (Drost et al. 1999b; Brown et al., 1999). Moderately low erucic acid (0.5 to 2.7%), and low p-hydroxybenzyl glucosinolate (0.0 to 0.1 μmoles per g seed) S. alba from crosses between moderately low erucic acid and low p-hydroxybenzyl glucosinolate S. alba lines have been developed (Raney et al. 1995a; Brown et al., 1999) towards the objective of obtaining an S. alba that can produce a canola-quality type low in erucic acid oil and low in glucosinolate canola-quality high protein meal. The amount of oleic acid within oil obtained from these oilseeds ranges from 54 to 72%. Any increase in the levels of oleic acid in seed oil of S. alba is desirable for human consumption. It is also desired that the levels of linolenic acid be low as this component is known to reduce the stability of the oil (White and Miller 1998; Scarth et al., 1994; Eskin et al. 1989; Przybyski et al. 1993; Prevot et al., 1990). Furthermore, reduction in the glucosinolate content within oil seeds ensures high value use of the seed meal obtained following oil extraction.
Despite all these efforts, the need remains for a S. alba line which combines superior edible oil quality (high oleic acid, low linolenic acid) with the lowest possible glucosinolate content. Similarly, for industrial applications, there is a need for a S. alba line from which oil seed comprising high erucic acid, and low glucosinolate content may be obtained. Furthermore to be acceptable as an oilseed crop, the line must have a high oil content, it must be genetically stable for these traits, and it must retain the positive agronomic attributes of S. alba, such as adaptation to dryland agriculture and resistance to diseases and pests, in combination with acceptable seed yields.
It is an object of the invention to overcome disadvantages of the prior art.
The above object is met by the combinations of features of the main claims, the sub-claims disclose further advantageous embodiments of the invention.